This invention relates to a brake mechanism for a conveyor idler, and to a kit of parts for a brake mechanism for a conveyor idler.
Typically a conveyor belt arrangement includes a conveyor belt supported on a series of conveyor idlers located along the length of the conveyor belt. Conveyor idlers are also referred to as conveyor rollers and, in this specification, a reference to a conveyor idler includes a reference to a conveyor roller. In the art it is known to drive the conveyor belt via a motor so that the conveyor belt runs on the conveyor idlers which are rotatably connected to a support frame.
The conveyor idlers typically do not include braking means and run freely in both a forward or reverse direction. This can create problems, especially with inclined conveyor belt arrangements. If the conveyor belt snaps, or the motor trips, then the conveyor belt may move in the reverse direction under the load on the conveyor belt. This will result in the load being deposited at the back of the conveyor belt arrangement which creates a safety hazard for employees, can cause damage to surrounding structures and results in production downtime.
Brake mechanisms for conveyor belts are known, but these are usually separate mechanisms which act on the conveyor belt itself and are located adjacent the conveyor belt where they are easily damaged. In addition, because these brake mechanisms are exposed they require regular maintenance. These brake mechanisms are relatively expensive. Furthermore, if the conveyor belt breaks, then these brake mechanisms, known as hold-backs, cannot prevent the conveyor belt and its load from running backwards.
U.S. Pat. No. 1,437,718 describes a cane carrier consisting of a flexible endless conveyor having two parallel spaced endless chains with slats extending between the two endless chains. Two dogs or cams are pivotally located above the slats. The dogs have teeth which permit movement of the upper flight in the upward direction, but prevent downward movement of the upper flight by digging into the slats. The cane carrier also has two sprockets which mesh with the upper and lower flights of the two endless chains. Associated with each sprocket is a ratchet and pawl which permits the sprocket to rotate in one direction only. The sprockets thus allow the upper flights to move upwardly but not downwardly, and prevent the lower flights from moving when the pawls are engaged with their sprockets.
U.S. Pat. No. 4,548,316 describes a conveyor holdback or conveyor run-back stop mechanism. The holdback is interposed between a drive motor and a gearbox. The holdback has a one-way ratchet arrangement which permits a drum around which the conveyor belt is looped to rotate in one direction only. Provided the conveyor belt does not break, the holdback will prevent the conveyor belt from running backwards.
DE 864978 also describes a holdback which is located on a fast turning drive shaft to a gearbox. This holdback also prevents the conveyor belt from running backwards.
It is desirable to have a conveyor idler which incorporates a braking mechanism which is not exposed to the elements, permits rotation of the conveyor idler in a forward direction, and retards rotation of the conveyor idler in a reverse direction thereby providing a braking effect on the conveyor belt.
According to a first aspect of the invention there is provided a brake mechanism for a substantially hollow conveyor idler which is rotatable about an idler shaft, the brake mechanism comprising:
a brake guide secured to the idler shaft and defining an outer surface adapted to fit rotatably within the hollow conveyor idler, the outer surface including at least one recess thereon; and
a brake element located in the recess, between an inner surface of the conveyor idler and the brake guide, and movable in the recess, between a first position and a second position;
wherein the recess is shaped such that in the first position the brake element is received substantially within the recess and in the second position the brake element protrudes from the recess and engages the inner surface of the conveyor idler.
Preferably the at least one recess defines a brake surface along which the brake element is moveable between the first and second positions.
Typically the brake guide is cylindrical and the outer surface of the brake guide is substantially complemental to the inner surface of the conveyor idler. Conveniently the brake guide defines a cylindrical surface and at least one end surface and at least one recess is located on the cylindrical surface. Optionally at least one recess is located on the end surface.
The brake element may be spherical. Alternatively the brake element may be cylindrical.
Ideally the brake guide includes a plurality of recesses located at regular intervals on the outer surface.
According to a second aspect of the invention there is provided a kit of parts for a brake mechanism for a hollow conveyor idler which is rotatable about an idler shaft, the kit comprising:
a brake guide securable to the idler shaft and defining an outer surface adapted to fit rotatably within the hollow conveyor idler, the outer surface including at least one recess thereon; and
a brake element locatable in the recess, between an inner surface of the conveyor idler and the brake guide, and movable in the recess, between a first position and a second position;
wherein the recess is shaped such that in the first position the brake element is received substantially within the recess and in the second position the brake element protrudes from the recess to engage the inner surface of the conveyor idler.
The brake element may be a ball bearing. Alternatively the brake element may be an elongate roller bearing.
According to another aspect of the invention a conveyor idler includes a sleeve having an outer surface and inner surface, a shaft about which the sleeve can rotate in a forward direction, a locking mechanism for preventing the sleeve from rotating in a reverse direction, but which locking mechanism permits rotation of the sleeve in the forward direction, the locking mechanism being located within the sleeve and having a shaft member which is fixed to the shaft and a rotatable member which is fixed directly or indirectly to the sleeve so that the rotatable member is rotatable with the sleeve in the forward direction, at least one locking member being interposed between the shaft member and the rotatable member so that the at least one locking member can lock the rotatable member to the shaft member to prevent the sleeve from rotating in the reverse direction but which locking member permits the rotatable member to rotate relative to the shaft member in the forward direction.
In the preferred form of the invention the at least one locking member is movable between an unlocked position in which the sleeve can rotate in the forward direction and a locked position in which it prevents the sleeve from rotating in the reverse direction.
The shaft member is preferably located within the rotatable member. However, the shaft member may be axially spaced from the rotatable member, with the rotatable member being fixed to an end cap which is in turn fixed to the sleeve so that the end cap is rotatable with the sleeve.
In one form of the invention a plurality of locking members may be provided.
The shaft member preferably has two side faces and an outer surface with a plurality of circumferentially spaced ramps on the outer surface, with locking members located on at least some, and preferably on all, of the ramps, and wherein the rotatable member defines a race with the locking members being sandwiched between the race and the ramps of the shaft member, and wherein the locking members are movable along their ramps between locked and unlocked positions.
The shaft member preferably has at least six ramps. In one form of the invention eight ramps are provided. In the preferred form of the invention ten ramps are provided.
The shaft member is preferably fixed to the shaft by being keyed to a keyway in the shaft with a key.
The shaft member is preferably made of a harder material than the rotatable member. The shaft member may be at least 50% harder than the rotatable member. Preferably the shaft member is at least 75% harder than the rotatable member. In one form of the invention the shaft member is 96% harder than the rotatable member. The rotatable member may be made of mild steel (EN8) which has a Rockwell hardness of 28, and the shaft member may be hardened to 55 Rockwell.
The locking members may be ball bearings or roller bearings. The locking members are preferably harder than the shaft member and harder than the rotatable member. In one form of the invention the locking members have a hardness of 60 Rockwell.
The rotatable member preferably has an outer surface with a diameter slightly less than the diameter of the inner surface of the sleeve. The rotatable member preferably also has two opposed side faces between which the shaft member and the locking members are sandwiched. A spacer may be interposed between each side face on the one hand, and the shaft member and the locking members on the other hand. Each spacer is preferably annular with an inner raised portion which abuts the shaft member. The spacers are preferably made of a polymeric material. In one form of the invention they are made of nylon.
The race of the rotatable member preferably includes a groove for the locking members to increase the contact area between the locking members and the rotatable member.
The rotatable member is preferably fixed to the sleeve by being welded to the inner surface of the sleeve by a weld or welds.